The present invention relates to a method for determining a rotor position of a synchronous motor. The present invention also relates to a data carrier with a computer program stored thereon for performing method, as well as to a computer with a program memory for storing the computer program. The present invention further relates to a machine-tool or production machine with the computer, wherein the computer can be implemented as a controller. In the following description, the term “production machine” is used in a generic sense and also includes robots which generally follow the concepts outlined here.
Several conventional methods are known for determining the position of a rotor of a synchronous motor relative to the stator of the synchronous motor in order to determine the electrical commutation of the motor without requiring a position measuring device to provide position information. Many of these methods are based on complex measurements of the inductances of the motor, or on measuring and determining the electromotive counterforce. Such methods make it possible to operate a synchronous motor without employing a position measuring device.
If the rotor position angle is only determined during ramp-up or start-up of the synchronous motor, for example for determining an offset between the zero position of the position measuring device and the rotor or for moving the rotor to a reference point, then less complex methods can be used to determine the rotor position.
German patent publication DE 102 15 428 A1 describes a method for determining the rotor position of a synchronous motor, whereby a plurality of current vectors is applied to the synchronous motor in different directions and the absolute value of the current vector necessary for obtaining a defined excursion of the rotor is determined. The motor position is subsequently computed from at least one angular position of the current vector, at which the absolute value of the current vector necessary for achieving the defined excursion is at a minimum. However, the curve describing the absolute value of the current vectors is very flat particularly in the vicinity of the minimum absolute values of the current vectors and the measured values have superimposed disturbances in practical applications. As a consequence, the motor position cannot be adequately determined.
It would therefore be desirable and advantageous to provide a method for determining the rotor position of a synchronous motor, which obviates prior art shortcomings and is specifically capable of accurately determining the rotor position in spite of existing disturbances and the flatness of the curve of the absolute value of the current vector.